This proposal seeks to understand the in vivo functions of endogenously expressed interleukin-1 receptor antagonist (IL-1ra). Mice lacking IL-1ra (gene knockouts) and mice over expressing IL-1ra (transgenics) will be characterized. These mutant mice to wildtype littermate controls. The proposed experiments will further analyze the underlying cellular and molecular physiological responses to the different levels of IL-1ra expression that occur in these mice. Changes in cytokine profiles will be analyzed as will leukocyte proliferation and migration. These studies will provide a deeper understanding of the in vivo mechanisms that respond to IL-1ra and provide clear phenotypes that can be used as genetic markers in a set of epistasis experiments. Double and triple mutants will be constructed involving the IL-1ra knockouts and overexpressors, IL-1 receptor nulls, IL-1beta TAbetas114 knockouts and caspase-1 (ICE) knockouts, in order to define the interactions between members of the IL-1/IL-1ra pathway. These epistasis experiments are intended to determine which phenotypes are due to the intracellular versus the secreted forms of IL-1ra, and to resolve whether another target exists for IL-1ra in addition to the IL-1 receptor, which the phenotypes of the single mutants currently strongly suggest.